Field of the Invention
An embodiment relates to a sheet conveyance apparatus for conveying a sheet and an image forming apparatus including the sheet conveyance apparatus.
Description of the Related Art
An image forming apparatus, such as an electrophotographic copying machine and an electrophotographic printer, includes an apparatus for switching the sheet conveyance direction at a branching portion between sheet conveyance paths. Such a switching apparatus provided with a guide member at the branching portion, where the position of the guide member is switched by a plunger type solenoid, is known. As a switching apparatus, a gate type sheet conveyance path switching apparatus is widely used. In the switching apparatus, the entrance of a conveyance path different from a selected conveyance path is closed, and a sheet is fed to the selected conveyance path. A plunger type solenoid is composed of a slidable iron core and a wire wound around the iron core in coil form. When a current is supplied to the wire, a magnetic field is generated to slide the iron core.
In an image forming apparatus, a guide member is provided at a branching portion between a sheet discharge conveyance path communicating with a discharge tray and a sheet reversing conveyance path communicating with a reversing tray. The guide member stands by being urged in one direction by a tension spring. The plunger type solenoid and the guide member are connected with each other via a link member. The plunger type solenoid is not supplied with a current. In this state, a conveyed sheet is guided to the sheet discharge conveyance path. When the plunger type solenoid is supplied with a current, the plunger slid by the absorption force generated by electromagnetic power and the guide member is rotated (swung) via the link member. At the time of two-sided conveyance, the plunger type solenoid repetitively turns ON and OFF to control the guide member to suitably switch the sheet conveyance direction.
Japanese Patent Application Laid-Open No. 2009-120345 discusses an apparatus having a similar configuration to the above-described configuration in which conveyance paths are switched therebetween by a plunger type solenoid. The technique discussed in Japanese Patent Application Laid-Open No. 2009-120345 aims at reducing abnormal sound occurring when a guide member is rotating. More specifically, the apparatus decreases the rotational (swinging) speed at which the guide member contacts an abutting portion by switching a current supplied to the solenoid, thus restricting collision sound.
In recent years, noise reduction is demanded while the operation speed of printers has been increased. Accordingly, there is a demand for shortening the distance between sheets (hereinbelow, referred to as a “sheet interval”) in continuous sheet conveyance (sheet interval reduction) to increase the number of sheets printed per minute to a maximum extent without increasing the number of rotations of a driving rotator such as a motor as much as possible. When performing two-sided printing with paper feed at shortened (reduced) sheet intervals (short sheet interval feed), is necessary to operate the guide member at short sheet intervals. When switching the guide member by using a plunger type solenoid, the following issues may arise.
For example, if the sheet interval is extremely reduced, it becomes difficult to switch the guide member between sheets. Conventionally, the time required for the sheet interval was longer than the switching time of the guide member. Therefore, it was possible to switch the guide member after the preceding sheet passes and to complete the switching operation before the following sheet reaches the guide member. However, in a case of sheet conveyance at short sheet intervals of about 30 milliseconds (ms), for example, it is very difficult to start and complete the guide member operation in such a short time.
As a method for reliably switching between sheet conveyance paths in conveyance at short sheet intervals, there is proposed a technique for starting the guide member operation while the preceding sheet is being conveyed. If the timing of starting the guide member operation brought forward in this way, most of the rotation operation of the guide member is completed at the timing when the trailing edge of the preceding sheet passes the leading end of the guide member. After the trailing edge of the preceding sheet passes the guide member, when the guide member performs the remaining rotation operation, the conveyance path switching is completed.
Suppose an example case where the timing of starting the guide member operation by a plunger type solenoid is brought forward and the guide member stands by in contact with the preceding sheet. After the trailing edge of the preceding sheet passes the guide member, when the guide member rotates by the sheet thickness, the preparation for guiding the following sheet toward the other conveyance path is completed. Therefore, although the conveyance path switching operation is reliably completed even at very short sheet intervals, the guide member switched by the plunger type solenoid contacts the sheet being conveyed with a comparatively strong force, fixed image is strongly rubbed, possibly resulting in an image failure.
Using a plunger type solenoid has an issue of difficulty in setting and managing the absorption force since the absorption force of the solenoid serves as a sheet contact pressure.